Inequalities

Algebra Level pending

Solve for x x where:

x 2 1 + x 2 4 > 3 \large |x^{2}-1|+|x^{2}-4|>3

If your solution set is of the form ( , a ) ( c , d ) ( e , ) (-\infty,a)\cup(c,d)\cup(e,\infty) , find a + c + d + e |a|+|c|+d+e .


The answer is 6.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Let f ( x ) = x 2 1 + x 2 4 f(x) = |x^2-1|+|x^2-4| , which is an even function. Therefore, we need only to consider for x 0 x \ge 0 and reflect the solutions in x 0 x \le 0 . There are three cases to be considered.

For 0 x < 1 0 \le x < 1 ,

f ( x ) = 1 x 2 + 4 x 2 = 5 2 x 2 5 2 x 2 > 3 x < 1 \begin{aligned} f(x) & = 1-x^2 + 4-x^2 \\ & = 5-2x^2 \\ 5-2x^2 & > 3 \\ \implies x & < 1 \end{aligned}

For 1 x < 2 1 \le x < 2 , f ( x ) = x 2 1 + 4 x 2 = 3 < 3 \begin{aligned} f(x) & = x^2-1 + 4-x^2 = 3 \color{#D61F06}< 3 \end{aligned}

For x 2 x \ge 2 ,

f ( x ) = x 2 1 + x 2 4 = 2 x 2 5 2 x 2 5 > 3 x > 2 \begin{aligned} f(x) & = x^2-1 + x^2-4 \\ & = 2x^2-5 \\ 2x^2-5 & > 3 \\ \implies x & > 2 \end{aligned}

Reflecting the solutions in x 0 x \le 0 , we have x 2 1 + x 2 4 > 3 |x^2-1|+|x^2-4| > 3 , for x ( , 2 ) ( 1 , 1 ) ( 2 , ) x \in (-\infty, -2) \cup (-1,1) \cup (2, \infty) . a + c + d + e = 2 + 1 + 1 + 2 = 6 \implies |a|+|c|+d+e = |-2|+|-1|+1+2 = \boxed{6}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...